1. Field of the Invention
The present invention relates to an intake device for a multi-cylinder engine.
2. Description of Prior Art
A conventional intake device for a multi-cylinder engine has a slow port formed in a ceiling wall of a mixing passage of a carburetor. According to this intake device, there is a likelihood that liquid fuel overflowed on a ceiling wall surface of the mixing passage from the slow port is blown downstream along an inner wall surface of the mixing passage. However, the conventional intake device lacks a means which accelerates atomization of the liquid fuel to be blown downstream from the slow port of the ceiling wall. This entails a case where the liquid fuel flows, as it remains liquid, into each of intake ports formed within a cylinder head. In this case, the fuel is distributed to respective cylinders non-uniformly to result in excessive or insufficient fuel supply. This causes mis-ignition or increases CO concentration in the exhaust gas.
Further, most of conventional intake devices each attaches a carburetor to a cylinder head through an intake manifold. Thus the carburetor projects from the cylinder head largely, which causes an engine to become large.
The present invention has an object to provide an intake device for a multi-cylinder engine, which can solve the foregoing problems.
An invention of claim 1, as exemplified in FIG. 1(B) or FIG. 3(B), forms a slow port 6 in a ceiling wall 4b of a mixing passage 4 so as to face downwards and has a peripheral wall of a fuel-air mixture passage portion 7a positioned downstream of the slow port 6 and upstream of a fuel-air mixture inlet 10, which peripheral wall is provided with a liquid fuel receiver 31. Therefore, it has the following advantage.
Fuel oil drops which fall down from the slow port 6 are involved in a current of a fuel-air mixture passing through the mixing passage 4 to accelerate their atomization. The liquid fuel overflowed on a ceiling wall surface of the mixing passage 4 from the slow port 6 is atomized to a certain degree while it is blown downstream along an inner wall surface of the mixing passage 4. The remaining liquid fuel not atomized while it is blown downstream is received by the liquid fuel receiver 31 to accelerate its atomization owing to the action of the mixture current. As such, the liquid fuel which has flowed out of the slow port 6 of the ceiling wall 4b of the mixing passage 4 accelerates its atomization before it reaches the mixture inlet 10 of a cylinder head 23 illustrated in FIG. 1(A) or FIG. 3(A). This can uniformly distribute the fuel from the mixture inlet 10 to respective intake ports 12,12 through branched passages 11,11, thereby inhibiting occurrence of the disadvantages caused by the non-uniform distribution of the fuel to respective cylinders, such as mis-ignition and increase of CO concentration in the exhaust gas.
The invention of claim 1, as exemplified in FIG. 1(A) or FIG. 3(A), has the branched passages 11,11 provided within the cylinder head 23. This dispenses with the intake manifold to result in the possibility of decreasing the projection of the carburetor 1 from the cylinder head 23 in an attempt to downsize the engine.
According to an invention of claim 2, as exemplified in FIG. 1(B) or FIG. 3(B), the liquid fuel receiver 31 comprises a groove 8 formed by concaving a ceiling wall 7b of the mixture passage portion 7a. Therefore, it has the following advantage.
In the case where the mixture current flows at a relatively high speed, most of the liquid fuel overflowed on a ceiling wall surface of the mixing passage 4 from the slow port 6 is blown downstream along the ceiling wall surface of the mixing passage 4. The liquid fuel not atomized while it is blown downstream flows into the groove 8 provided in the ceiling wall 7b of the mixture passage portion 7a and is received here to accelerate its atomization with the action of a negative pressure produced by the mixture current passing by the vicinity of an opening of the groove 8.
According to an invention of claim 3, as exemplified in FIG. 1(A) or FIG. 3(A), the liquid fuel receiver 31 further includes grooves 8,8 formed by concaving left and right both side walls 7c,7c of the mixture passage portion 7a. Therefore, it has the following advantage.
In the case where the mixture current flows at a relatively low speed, most of the liquid fuel overflowed on the ceiling wall surface of the mixing passage 4 from the slow port 6 is blown downstream first along the ceiling wall surface of the mixing passage 4 and then along left and right both side wall surfaces of the mixing passage 4 while it is gradually falling down by its own weight. The liquid fuel not atomized while it is blown downstream flows into the grooves 8,8 formed in the left and right both side walls 7c,7c of the mixture passage portion 7a and is received here to accelerate its atomization with the action of a negative pressure produced by the mixture current passing by the vicinity of an opening of each of the grooves 8,8.
According to an invention of claim 4, as exemplified in FIG. 1(B) or FIG. 3(B), the liquid fuel receiver 31 comprises a wall 9a projecting from the ceiling wall 7b of the mixture passage portion 7a. This wall 9a forms a throttle hole 9 for the mixture. Therefore, it has the following advantage.
The liquid fuel not atomized while it is blown downstream along the ceiling wall surface of the mixing passage 4 is received by the wall 9a projecting from the ceiling wall 7b of the mixture passage portion 7a to accelerate its atomization with the action of a negative pressure produced by the mixture current passing through the throttle hole 9.
According to an invention of claim 5, as exemplified in FIG. 1(A) or FIG. 3(A), the liquid fuel receiver 31 further includes walls 9a,9a projecting from the left and right both side walls 7c,7c of the mixture passage portion 7a. These walls 9a,9a form a throttle hole 9 for the mixture. Therefore, it has the following advantage.
The liquid fuel not atomized while it is blown downstream along left and right both side wall surfaces of the mixing passage 4 is received by the walls 9a,9a projecting from the left and right both side walls 7c,7c of the mixture passage portion 7a to accelerate its atomization with the action of a negative pressure produced by the mixture current passing through the throttle hole 9.
According to an invention of claim 6, as exemplified in FIG. 1(B) or FIG. 3(B), the liquid fuel receiver 31 comprises a groove 8 formed by concaving the ceiling wall 7b of the mixture passage portion 7a and a wall 9a projecting from the ceiling wall 7b of the mixture passage portion 7a. This wall 9a forms a throttle hole 9 for the mixture. Therefore, it has the following advantage.
The liquid fuel not atomized while it is blown downstream along the ceiling wall surface of the mixing passage 4 flows into the groove 8 formed in the ceiling wall 7b of the mixture passage portion 7a. Although, in some cases, the liquid fuel which has flowed into the groove 8 may tend to flow downstream out of the groove 8 as it remains liquid, with the action of a negative pressure produced by the mixture current passing by the vicinity of an opening of the groove 8, it is assuredly received by the wall 9a to accelerate its atomization with the action of a negative pressure produced by each of the mixture current passing by the vicinity of the opening of the groove 8 and the mixture current passing through the throttle hole 9.
Even if the wall 9a has a height increased so as to receive the liquid fuel reliably, its projection can be decreased by an amount corresponding to the existence of the groove 8. This inhibits a throttling resistance of the throttle hole 9 from increasing more than necessary to result in the possibility of securing a high output.
According to an invention of claim 7, as exemplified in FIG. 1(A) or FIG. 3(A), the liquid fuel receiver 31 further includes grooves 8,8 formed by concaving the left and right both side walls 7c,7c of the mixture passage portion 7a as well as walls 9a,9a projecting from the left and right both side walls 7c,7c of the mixture passage portion 7a. Therefore, it has the following advantage.
The liquid fuel not atomized while it is blown downstream along the left and right both side wall surfaces of the mixing passage 4 flows into the grooves 8,8 provided in the left and right both side walls 7c,7c of the mixture passage portion 7a and is received by the walls 9a,9a surely. Further, even if each of the walls 9a,9a has its width increased, its projection can be decreased by an amount corresponding to the existence of each of the grooves 8,8.
According to an invention of claim 8, as exemplified in FIGS. 1(A) and 1(B) or FIGS. 3(A) and 3(B), the mixing passage 4 has an outlet 4a communicated with the mixture inlet 10 through an insulator 7. The liquid fuel receiver 31 is formed within this insulator 7. Therefore, it has the following advantage.
The molding die for the insulator 7 has a structure simpler than those of the molding dies for a mixing body 1a of the carburetor 1 and for the cylinder head 23. Accordingly, when compared with the case of providing the mixing body 1a or the like with the liquid fuel receiver 31, less trouble occurs on processing or cutting the molding die for forming the liquid fuel receiver 31.
According to an invention of claim 9, as exemplified in FIGS. 1(A) and 1(B) or FIGS. 3(A) and 3(B), the insulator 7 has a length (L1) smaller than a length (L2) between the slow port 6 and the outlet 4a of the mixing passage 4. Therefore, it has the following advantage.
Since the insulator 7 is short, it does not increase a mixture-flow resistance more than necessary and besides can decrease the projection of the carburetor 1 from the cylinder head 23 in an attempt to downsize the engine.
An invention of claim 10, as exemplified in FIG. 1(A) or FIG. 3(A), makes an axis 5a of a throttle valve 5 substantially horizontal and forms the branched passages 11,11 in the shape of a letter xe2x80x98Vxe2x80x99. Therefore, it has the following advantage.
The mixture is uniformly distributed in a left and right direction from the throttle valve 5 toward the mixture inlet 10 to result in being uniformly distributed into respective intake ports 12,12 through the V-shaped branched passages 11,11 from the mixture inlet 10. In consequence, it can accelerate uniformization of the mixture to be distributed to respective cylinders.
An invention of claim 11, as exemplified in FIGS. 1(A) and 1(B) or FIGS. 3(A) and 3(B), steps the groove 8 from an opening edge of the outlet 4a of the mixing passage 4. Therefore, it has the following advantage.
The liquid fuel not atomized while it is blown downstream along the ceiling wall surface of the mixing passage 4 as well as the left and right both side wall surfaces thereof flows into the groove 8 just after it has flowed out of the outlet 4a of the mixing passage 4. Accordingly, the liquid fuel makes a prompt atomization.
An invention of claim 12, as exemplified in FIG. 3(B), does not project the wall 9a from a bottom wall 7d of the mixture passage portion 7a. Therefore, it has the following advantage.
The throttling resistance of the throttle hole 9 does not increase more than necessary due to the absence of the projection of the wall 9a from the bottom wall 7d.